USPTO Patents Application 10687850

J

Europalsches Patentamt

® 0))) European Patent Office © Publication number: 0171239

Office europ6en des brevets A1

®

@ Application number: 85305345.2
@ Date of filing: 26.07.85

EUROPEAN PATENT APPLICATION

® intciv h 01 T 19/00

© Priority: 26.07.84 JP 156937/84

® Date of publication of application: 12.02.86
Bulletin 86/7

® Designated Contracting States: DE FRGB TT

© Applicant: Nippon Paint Company, Ltd, 2-1-2, Oyodoklta
Oyodo-ku, Osaka-shi Oseka-fu (JP)
Applicant: SANKYO DENGYO COMPANY, LIMITED,
14-13, Hon-cho 1-Chome, Nakano-ku Tokyo (JP)

@ Inventor: Ikeda, Shojl, 2-503, 67, Nlshlmachl, Ikaga,
Hirakata-Bhl Osaka-fu (JP)

Inventor: Tsutsul, Koichl, 5-chome, 13-4, Osumlgaoka

Tanabe-cho, Tsuzukl-gun Kyoto-fu (JP)

Inventor: Saitoh, Toshryukl, 3-7-26, Hon-cho, Ageo-shl

Saftama-ken(JP)

Inventor: Inagakl, Tauguya, Tokochl-Danchl 5-542 2469,
Nagatauda-cho Mldori-ku, Yokohama-shI Kanagawa-ken
(JP)

@ Representative: Perry, Robert Edward et al, GILL
JENNINGS & EVERY 53-64 Chancery Lane, London
WC2A1HN(GB)

@ Apparatus and method for surface treatment

® Apparatus suitable for use in the surface treatment of an
article (6), in which the apparatus comprises two opposing
electrodes (1,2) and means for applying a high-voltage differ-
ence and thereby activating the surface of an article (6) dis-
posed between the electrodes (1,2), characterised in that one
of the electrodes (1) includes a flexible contact member (3)
which can follow the contours of the article (6).

The apparatus can be used to activate the surface of the
article (61, e.g. if the article (6) and the contact member (3) are
moved relative to each other. Activation is preferably in a
plasma.

0>

iu

ACTORUM AG

NIPPON/SANKYO '

-1-

0171239

70/2491/02

APPARATUS AND METHOD FOR SURFACE TREATMENT
The present invention relates to an apparatus and a
method for surface treatment. In particular, the
invention relates to surface treatment in the plasma
state, for uniformly and rapidly obtaining physical and
chemical modifications of the surfaces of articles such
as plastics, fibrous products and moulded items of, say
paper or wood, under various gases and at various
temperature and pressure conditions.
10 It is known to modify the physical properties of

articles as described above, e.g. in order to improve
surface adhesion, coating, bonding, wettability or
durability, by chemical methods, e.g. by using acid,
alkali, ultra-violet irradiation or flame treatment.
These methods have both merits and demerits. For
example, chemical treatment has the drawback of
complexity, since a wet process is required. Further
ultra-violet irradiation is not suitable for treating
articles having irregular contours. Moreover, flame
treatment is limited in applicability owing to the high
temperatures to which the articles must be exposed.

Surface treatment methods using plasma are
potentially both convenient and effective.
Sub-atmospheric pressure plasma treatment is widely used,
but the need for reduced pressure is inconvenient when
the article is large in size, and the technique requires
careful sealing of the surface treatment apparatus.

According to a first aspect of the present
invention, for use in the surface treatment of an
artxcle, apparatus comprises two opposing electrodes and
means for applying a high voltage difference and thereby
activating the surface of an article disposed between the
electrodes, in which one of the electrodes has a flexible
contact member which can follow the contours of such an
JD article.

0171239

According to a second aspect of the present
invention, a method for activating the surface of an
article comprises disposing the article between two
opposing electrodes and applying a high voltage
5 difference between the electrodes, in which one of the
electrodes has a contact member which is in contact with
the article and which is flexible to the extent that it
can follow the contours of the article.

Of the two opposing electrodes, either the one

10 including the contact member or the other may be termed
the "excitation" electrode. The electrode which does not
include the contact member may be formed of an
electrically-conductive material such as metal or carbon,
and may have any suitable configuration such as that of a

15 plate or cylinder, depending on the contour of the
article to be treated; preferably > it carries a
dielectric layer on its surface, in order to prevent
local concentration of the electric field, and to ensure
uniform treatment of an article. The dielectric layer

20 may be made of, for example, glass, ceramics, enamel,
asbestos, marble, slate, mica or plastics, e.g. epoxy
resin, polyimide nylon or fluorine plastics such as
2-vinylidene fluoride 4-ethylene fluoride 6-propylene
fluoride copolymer or 4-ethylene fluoride perfluoro-

25 alkoxy copolymer. The thickness of the dielectric layer
can be selected according to the overall requirements for
the apparatus, but' is preferably 0.1 to 10 ram.

The means for applying the necessary voltage can be
any conventional supply circuit. It is- desirable that

30 the supply circuit should be capable of controlling
arbitrarily, in accordance with a load, the discharge
current for producing plasma*, and should be capable of
frequency adjustment and high-voltage power output, to
respective optimum levels. For example, a stabilising

35 power source may be used, together with a detector for

0171239

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10

15

20

25

30

35

detecting electric current and voltage, and a control
device for controlling the high-voltage power source.
Signals indicative of the electric current and the
voltage are fed back to the control device from the
detector, thereby allowing output electric current and
output voltage to be optimised in accordance with loads
applied between the electrodes. The use of a stabilising
power source makes it possible to treat articles having
complicated contours uniformly, in the plasma state.

The voltage is usually from 10 to 50 kv and
preferably from 10 to 30 kV. The frequency for the power
source is preferably from 1 to 100 kHz.

The flexible contact member may be in the form of
fibres, a sheet, cloth or leaf, it may consist of a
known good conductor such as a metal or carbon. Specific
examples of suitable contact members are electrically-
conductive fibres, aluminium foil, steel wire, stainless
steel wire, stainless steel fibre, stainless steel cloth
stainless steel web. stainless steel felt, brass wires
copper wires, copper foil and carbon fibre cloth.

The contact member may be formed of a composite of a
conductor and an insulator. For example, it may comprise
rubber having a high content of carbon or metal powder,
electrically-conductive plastics, metal-plated fibres or
composite fibres comprising core and sheath portions, the
sheath being a synthetic fibre and the core including an
electrically-conductive layer having a large content of
metal powder or carbon.

The contours of the contact member, especially its
radius of curvature at its distal end, are important in
thexr effect on the type and stability of the electrical
discharge. As the radius of curvature at the distal end
decreases, more stable plasma can be obtained at low
voltages, but damage and electrical disconnection of the
contact member can take place more readily. The

0171239

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preferred radius of curvature at the distal end of the
contact member is 0,005 to 0.5 mm.

One specific example of a contact member is a
plurality of composite electrically-conductive fibres 50
5 urn in diameter and 100 mm long. The fibres are bonded to
an electrically-conductive base member by an
electrically-conductive bonding agent, and are pressed
into a brush-like configuration. A fibrous contact
member can also be obtained by similar arrangement of

10 plurality of tow- type stainless steel fibres , e.g. those
marketed under the trade name Naslon by Nihon Scisen Co.,
Ltd., Japan and now widely used iri the industry, or
twisted yarns.

Alternatively, a brush-like contact member having

15 relatively hard bristles can be made by using elastic
phosphor bronze wires cut to a length of 50 mm and
arranged in a sheet-like shape 1 mm thick. The diameter
of such wires is selected in accordance with their
electrical discharge properties and durability, and is

20 preferably 0.008 to 0.5 mm. A brush-like contact member
can be obtained by pressing end portions of the wires,
using a metal plate.

An alternative specific example of a contact member
for use in the invention comprises a plurality of

25 essentially rectangular sheets, e.g. aluminium foils 0.01
to 0.2 mm thick and 5 mm wide, secured to a metal plate.
A cloth-like contact member can be obtained by cutting a
carbon fibre fabric or a stainless steel cloth, web or
felt, e.g. to a thickness of 0.5 mm, and securing it to a

30 metal plate.

Iri use, the flexible contact member is usually
brought into wiping contact of the surface of the article
to be treated. It is therefore essential that the
flexibility. should be sufficient to avoid damage. In

35 order to improve the effect of the apparatus and method

0171239

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10

15

20

25

30

35

of the invention, it may be appropriate to use a
plurality of electrodes including flexible contact
members .

In general, the shape of the contact member will be
chosen having "regard to the contours of the article to be
treated. Further, the time of treatment will be chosen
according to the nature of the article to be treated, as
well as the applied voltage and frequency.

In order to obtain wiping contact of the flexible
contact member with the article to be treated, these two
.elements are displaced relative to one another. For
example, the electrodes may be stationary and the article
displaced. Alternatively, the electrode including the
flexible contact member may be moved while the article to
be treated is secured to the other electrode. The
relative motion may be linear, circular and/or rotary.
The motion can be constant or varied; variation may be
continuous or intermittent, depending on the nature of
the article, but in any case can be suitable for the
treatment of articles having complicated contours. If
the "wiping- speed of the contact member relative to the
article is 50 mm/s or less, however, the effect of
treatment is often reduced.

It is usually convenient and most desirable for the
article to be treated in atmospheric air under ambient
conditions. Depending on such factors as the adhesion
between the coating film and the surface being treated,
the coating itself, the bond, wettability and durability,
it may also be appropriate that one or more of such
various gases as nitrogen, oxygen (and especially
nitrogen and/or oxygen) , carbon dioxide, carbon monoxide,
ammonia, nitrogen oxide, halocarbons, vinyl compounds,
argon or helium are introduced into a chamber within
which the apparatus is contained. It may also be
suitable that a containing tank is hermetically sealed, so

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0171239

that the article can be treated at sub-atmospheric or
super-atmospheric pressure.

The article to be treated may be of an insulating
material. It may be of inorganic material such as glass,
mica or ceramics, an organic material such as paper,
organic fibres, cloth, wood or plastics such as a
polyolefin, acrylic or nylon material, or a composite
comprising both inorganic and organic materials of this
type .

The invention will now be described by way of
example only with reference to the accompanying drawings,
in which:

Figure 1 is a schematic view of one embodiment of
apparatus of the present invention;

Figure 2 is a schematic view of apparatus of the
invention in use;

Figure 3 is a perspective view of an article which
can be treated in accordance with the invention; and

Figures 4a to 4d are schematic views of embodiments
of flexible contact members which can be used in the
invention .

Figure 1 shows apparatus K including an upper
electrode 1 and, opposing the upper electrode 1, a lower
electrode 2. Here and in general, either of the two
electrodes can act as an "excitation " electrode.

The upper electrode 1 includes a flexible contact
member 3 in the form of a plurality of electrically-
conductive fibres. These fibres can follow the contours
of an article disposed between the electrodes.

The lower electrode 2 is formed of an electrically-
conductive material such as metal or carbon. A
dielectric layer 4 is provided on the surface of the
lower electrode 2.

Figure 1 shows also the electrical circuit by which
high voltage is applied between the electrodes 1 and 2,

0171239

-7-

and which comprises a stabilising power source 5, a
detector 5a for detecting electric current and voltage,
between the stabilising power source and the lower
electrode 2, and a control device 5b for controlling the
5 high-voltage power source 5. Signals indicative of the
electric current and the voltage are fed back to the
control device 5b from the detector 5a, and it is thus
possible arbitrarily to set the output electric current
and the output voltage at respective optimum values in
10 accordance with the loads applied between the electrodes
1 and 2.

In common with Fig. 1, Fig. 2 shows the electrodes 1
and 2, the flexible contact member 3 and the dielectric
layer 4. It shows also an article 6 which itself is
15 illustrated in greater detail in Fig. 3. With reference
to Fig. 2, the article 6 is treated by applying a voltage
and moving the article 6 relative to the contact member
3.

Fig. 4a shows a contact member 3 in the form of a
20 plurality of rectangular sheet-like members. Fig. 4b
shows a cloth-like contact member 3. Figs. 4c (1) and
4c (2) are, respectively, a front elevational view and a
bottom plan view of a fibrous (brush-like) contact member
3 composed of two coaxial circular bristle portions
25 intended to be rotated about the common axis. Figs.
4d(l) and 4d(2) are, respectively, a front elevational
view and a side elevational view of a fibrous
(brush-like) contact member 3 in which bristles extends
radially from, and axially along, a rod-like electrode 1;
30 it is intended that, in use, the electrode 1 and thus the
contact member 3 should be rotated about the axis of the
electrode 1.

35

The following Examples illustrate the invention,
with reference to the accompanying drawings.

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0171239

Example 1

A rectangular aluminium foil 100 mm wide was
suspended from an excitation electrode 1. An aluminium
plate 1 mm thick was employed as the opposite electrode
5 2, and to this was secured a sheet 6 of polypropylene , 45
mm wide. The electrode 2 and the sheet 6 were displaced
relative to the excitation electrode at 10, 5, 2.5 or
1.25 mm/s, such that the aluminium contact member 3 came
into wiping contact with the surface of the sheet. At

10 the same time, a voltage of 20 kV at a frequency of 5 kHz
was applied between the electrodes, to effect electrical
discharge such that plasma was produced.

After it had been treated in the plasma state by the
surface treating apparatus K, the polypropylene sheet was

15 subjected to spray-coating using a two-part liquid system
polyurethane . Its bonding strength was then examined by
the 180° peel test. The result was 1800, 1890, 2000 or
2040 g/cm, respectively, depending on the respective
displacement speed. By contrast, a sheet which has not

20 been treated by the surface treating apparatus K has a
peeling strength no more than 200 g/cm.
Example 2

A polypropylene sheet was treated in the plasma
state by the surface treating apparatus K, under the same

25 conditions as in Example 1, except that a cloth-like

contact member 3, formed from a carbon fibre fabric 50 mm
long, was employed.

The peel strengths for the four respective
displacement speeds were 1340, 1500, 1800 and 1870 g/cm.

30 it was thus observed once again that, with increasing
displacement speed and thus decreasing treatment time,
the peel strength is reduced. However, the value of 1340
g/cm, obtained at a displacement speed of 10 mm/s, is
sufficient for practical use.

35

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0171239

Example 3

A plate-like contact member 3, about 1 mm thick,
formed by bundling fibres each 100 mm long and 20 nm in
diameter, was employed. A member made of polypropylene,
which has a pair of flat portions B and an intermediate
raised portion A, as shown in Fig. 3, was treated in the
plasma state by the surface treating apparatus K in a
manner similar to that of Example 1. With respect to
Fig. 3, the dimensions D, H and W were 190 mm, 20 mm and
50 mm, respectively; the dimensions M, N and L were
respectively 70 mm, 70 ram and 70 mm or more.

The surface-treated plate member was subjected to
spray-coating as in Example 1. The bonding of the
portions A and B was examined by the 180° peel test, and
the results are given in Table 1. It is apparent that
there is substantially no difference in peeling strength
between the portions A and B, i.e. the plate member is
treated uniformly.

Table 1

Displacement Peel strength (g/cm)
(mm/sec.) A B

10 1750 1800

5 1890 1900

2.5 1950 1950

1.25 2000 2040

Example 4

A cloth-like contact member 3, formed from a
stainless steel cloth 0.5 mm thick, 70 mm long and 90 mm
wide was suspended from the excitation electrode 1. An
aluminium plate 5 mm thick was employed as the opposite
electrode 2, and to this was secured a sheet of
polypropylene, 60 ram wide. The electrode 2 and the sheet
6 were displaced relative to the excitation electrode at
23 mm/ s such that the contact member 3 came into wiping
contact with the surface of the sheet. At the same time,

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0171239

a voltage of 30 kV at a frequency of 5 kHz was applied
between the electrodes, to effect electrical discharge
such that plasma was produced.

After it had been treated in the plasma state up to
20 times by the surface treating apparatus K, the
polypropylene sheet was subjected to spray-coating using
a two-part liquid system polyurethane. Immediately after
drying of the spray-coating and after immersion of the
sheet in hot water (40 C) for 10 days. Its bonding
strength was examined by the 180° peel test. The results
are given in Table 2.

Table 2

No. of Peel strength Peel strength

treatments (Just after drying) (After immersion

(g/cm) in water)

(g/cm)

0 (untreated) <200 <200

4 450 . >200

12 485 >200

20 1140 650

Comparative Example

As in known surface treating apparatus, an aluminium
plate is employed in place of the excitation electrode
having the contact member 3 hung therefrom. A plate as
in Example 3 was treated in the plasma state by the known
surface treating apparatus in a manner similar to that of
Example 3, except that there was a distance between the
excitation electrode and the portion A, maintained at 3
mm. The electrode 2, having the plate member secured
thereto, was displaced relative to the excitation
electrode at 1.25 mm/s.

The bonding strength of the surface-treated plate
was examined by the 180° peel test. The projecting
portion A had a peel strength of 1370 g/cm, i.e. similar
to the values obtained in Examples 1, 2 and 3, but the
portions B had a peel strength no more than 200 g/cm.

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0171239

CLAIMS

1. Apparatus (K) suitable for use in the surface
treatment of an article (6) , in which the apparatus (K)
comprises two opposing electrodes (1,2) and means for
5 applying a high-voltage difference and thereby activating
the surface of an article (6) disposed between the
electrodes (1,2), characterised in that one of the
electrodes (1) includes a flexible contact member (3)
which can follow the contours of the article (6) .

10 2> Apparatus according to claim 1, in which the contact
member is in the form of a brush , sheet or cloth.
3. Apparatus according to claim 1 or claim 2, in which
the contact member is formed from stainless steel,
aluminium, brass or carbon.

15 4. Apparatus according to any preceding claim, in which
the electrode which does not include the flexible contact
member carries a dielectric layer on its surface.

5. Apparatus according to any preceding claim, in which
the electrode not including the flexible contact member

20 is made of stainless steel, aluminium, brass, iron or
copper .

6. Apparatus according to any preceding claim, which
additionally comprises means for moving the contact
member relative to an article to be treated,

25 7 # Apparatus according to any preceding claim, in which
the means for applying a high-voltage difference
comprises an electrical circuit adapted to provide a
current sufficient to effect an electrical discharge.
8. A method for activating the surface of an article

30 (6) , which comprises disposing the article (6) between
two opposing electrodes (1,2) and applying a high-voltage
difference between the electrodes (1,2), characterised in
that one of the electrodes (1) includes a contact member
(3) which is in contact with the article (6) and which is

35

0171239

-In-
flexible to the extent that it can follow the contours of
the article (6) .

9. A method according to claim 8, in which the article
is treated in oxygen or nitrogen or a mixture thereof.
5 10. A method according to claim 8 or claim 9, in which
the article is treated at a voltage of 10 to 50 kV and a
frequency of 1 to 100 kHz.

11. A method according to any of claims 8 to 10, in
which the article is a plastics of fibrous product or a

10 moulded product of paper or wood.

12. A method according to any of claims 8 to 11 , in
which the article is moved relative to the contact
member.

13. A method according to any of claims 8 to 12, which
15 comprises using apparatus according to any of claims 1 to

7.

20

25

30

0171239

Fig. I

/ It

V \

/ fH

f

0171239

Fig. 4 a

7

Fig. 4 b

Fig. 4c (I)

Fig. 4c (2)

Fig. 4d(l)

Fig. 4d (2)

j

European Patent
Office

EUROPEAN SEARCH REPORT

0171239

Application number

EP 85 30 5345

DOCUMENTS CONSIDERED TO BE RELEVANT

Category

EP-A-0 055 686 (HIRSCHINGER)

* Page 5, lines 24-28; page 6,
line 28 - page 7, line 33; figure
1; page 9, lines 8-11; figure 7;
page 10, lines 19-20 *

US-A-3 183 352 (BRANDT)

* Column 2, line 12 - column 3,
line 16; figures 1,2 *

Citation of document with indication, where appropriate,
of relevant passage*

US-A-4 275 301 (RUEGGEBERG)

* Column 2, lines 30-32; figure

1; column 3, lines 23-29 *

The present search report has been drawn up for all claims

Relevant
to claim

CLASSIFICATION OF THE
APPLICATION (Int CM)

1/2,4,
6-8,11
-13

3,5,10

1,2,6-
8, 11-
lS

3,10

H 01 T 19/00

TECHNICAL FIELDS
SEARCHED (Int. OA)

H 01 T

Place of search

THE HAGUE

Date of completion of the search

17-10-1985

IJN E.A.

Examiner

CATEGORY OF CITED DOCUMENTS

X : particularly relevant if taken alone

Y : particularly relevant if combined with another

document of the same category
A : technological background
O : non-written disclosure
P : intermediate document

T : theory or principle underlying the invention
E : earlier patent document, but published on, or

after the filing date
D : document cited in the application
L : document cited for other reasons

4 : member of the same patent family, corresponding
document